In an existing cellular communications technology, a user terminal communicates with a base station by using an air interface, and forwards user data to a destination node in a network through the base station.
A device-to-device (D2D) communications technology is a technology of direct communication between terminals. A difference from the existing cellular communications technology is that, data of user equipment does not need to be transmitted by a base station, but is transmitted directly by using an air interface between terminals, thereby reducing a delay of network forwarding. A typical application scenario is a public safety scenario, for example, communication between members of a fire alarm group.
A resource used by traditional user equipment for transmitting data may be scheduled by a base station in a cellular network. That is, the user equipment reports, to the base station by using a buffer status report (BSR), an amount of data waiting to be sent, and the base station schedules a data resource according to the BSR.
However, a D2D device may belong to multiple communications groups at the same time, for example, a device may belong to both a fire alarm group and a police group. When a D2D device needs to report buffer status reports of multiple different communications groups, a traditional BSR mechanism cannot be applied to a case in which there are multiple communications groups. That is, in the existing BSR mechanism, to-be-transmitted buffer data of multiple communications groups cannot be reported, and therefore a base station cannot schedule a resource for the D2D device.